1. Field of the Invention
The present invention relates to a motor control apparatus for a hybrid vehicle which carries a combustion engine and a motor.
This application is based on Japanese Patent Application No. 11-283579, the contents of which are incorporated herein by reference.
2. Description of the Related Art
To improve the driveability of a vehicle, a control apparatus, which can respond without delay to instructions from a driver to accelerate or decelerate the vehicle, is required. A hybrid vehicle which has a combustion engine and a motor must control without delay the amount of electric energy which is supplied to the motor, or which is drawn from the motor. The hybrid vehicle supplies the electric energy to the motor, and the motor assists the engine to accelerate the vehicle. Further, the hybrid vehicle uses the motor as a generator, and the generated electric energy is drawn so that the vehicle decelerates.
To achieve the control without delay, the gain supplied from the control apparatus to the motor may be increased, and, alternatively, the rate of change of electric energy per unit time drawn from the motor may be increased, and the rate of change of the motor torque per unit time may be increased.
To achieve the above-mentioned control, a structure for drawing and supplying the electric energy to the motor must be provided, and the structure may unbalance the energy management when the engine is idling, or when the vehicle is cruising at a constant speed. When the engine is idling, or when the vehicle is cruising, the motor acts as a generator to send the generated energy to the battery, and the battery is charged. The amount of electric energy stored in the battery cannot be accurately known only by detecting the electric energy which is supplied to or sent from the motor. The reason for this is that the battery is not only connected to the motor but also connected to various other electrical equipment which consumes electric energy, and that the electric energy supplied to and sent from the motor is not necessarily the same as that supplied to and sent from the battery.
To solve this problem, the electric energy supplied to and sent from the battery may be detected. However, according to the structure for detecting the electric energy and for controlling the detected value to maintain it at a fixed value, when the motor generates electric energy while the vehicle is idling or cruising, the motor generates the electric energy to be consumed by the electrical equipment such as the air conditioner, head lights, and defroster, and the electric energy to be supplied to the battery. Therefore, variations in the electric energy consumed by the electrical equipment appears as a variation in electric energy generated by the motor.
According to this structure, when electrical equipment is turned on or off while the engine is idling, the electric energy generated by the motor varies, the load on the engine also varies, and the engine may therefore stall.
Further, when electrical equipment is turned on or off while the vehicle is cruising, the electric energy generated by the motor varies, the load on the engine also varies, and the vehicle may behaves unstably.